Organization of spinal inputs to the perihypoglossal complex in the cat

Development of the human perihypoglossal nuclei from mid-gestation to the perinatal period: A morphological study

INTRODUCTION

Morphological data on the development of the human perihypoglossal nuclei (PHN) are scarce. This study describes the morphology of the human PHN from mid-gestation to the perinatal period.

MATERIALS AND METHODS

Ten brains were collected from infants aged 21-43 postmenstrual weeks (PW). Serial sections were cut and stained using the Klüver-Barrera method. Morphometric parameters [volume, neuronal numerical density (Nv) and total number (Nt), and neuronal profile area (PA)] were analyzed from microscopic observations.

RESULTS

Four PHN [nucleus of Roller (RO), interfascicular nucleus (IF), intercalated nucleus (IC), and prepositus nucleus (PR)] were identified at 21 PW. Medium-sized to large, oval, or polygonal neurons were concentrated in the ventral nuclei (RO and IF) and localized regions near the IC-PR transition of the dorsal nuclei (IC and PR). Small to large neurons of various shapes were scattered across the dorsal nuclei. The PR showed rostrocaudal differences in the neuronal cytoarchitecture. The volume of each nucleus increased between 21 and 43 PW, with a typical exponential increase for the dorsal nuclei. The Nv in each nucleus exponentially decreased, whereas the Nt was almost stable. The median PA linearly increased for every nucleus, and the increasing rates were greater for the ventral nuclei than those for the dorsal nuclei.

CONCLUSIONS

The dorsal and ventral PHN are identifiable at mid-gestation. The topographic relationships of the four nuclei are conserved until the perinatal period. The characteristic neuronal cytoarchitecture of each group is rapidly formed by 28-30 PW.

Upbeat vertical nystagmus after brain stem cavernoma resection: a rare case of nucleus intercalatus/nucleus of roller injury

INTRODUCTION

CNS cavernomas are a type of raspberry-shaped vascular malformations that are typically asymptomatic, but can result in haemorrhage, neurological injury, and seizures. Here, we present a rare case of a brainstem cavernoma that was surgically resected whereafter an upbeat nystagmus presented postoperatively.

CASE REPORT

A 42-year old man presented with sudden-onset nausea, vomiting, vertigo, blurred vision, marked imbalance and difficulty swallowing. Neurological evaluation showed bilateral ataxia, generalized hyperreflexia with left-sided predominance, predominantly horizontal gaze evoked nystagmus on right and left gaze, slight left labial asymmetry, uvula deviation to the right, and tongue deviation to the left. MRI demonstrated a 13-mm cavernoma with haemorrhage and oedema in the medulla oblongata. Surgery was performed via a minimal-invasive, midline approach. Complete excision was confirmed on postoperative MRI. The patient recovered well and became almost neurologically intact. However, he complained of mainly vertical oscillopsia. The videonystagmography revealed a new-onset spontaneous upbeat nystagmus in all gaze directions, not suppressed by fixation. An injury of the rarely described intercalatus nucleus/nucleus of Roller is thought to be the cause.

CONCLUSION

Upbeat nystagmus can be related to several lesions of the brainstem, including the medial longitudinal fasciculus, the pons, and the dorsal medulla. To our knowledge, this is the first case of an iatrogenic lesion of the nucleus intercalatus/nucleus of Roller resulting in an upbeat vertical nystagmus. For neurologists, it is important to be aware of the function of this nucleus for assessment of clinical manifestations due to lesions within this region.

The intercalatus nucleus of Staderini

Rutilio Staderini was one of the leading Italian anatomists of the twentieth century, together with some scientists, such as Giulio Chiarugi, Giovanni Vitali, and others. He was also a member of a new generation of anatomists. They had continued the tradition of the most famous Italian scientists, which started from the Renaissance up until the nineteenth century. Although he carried out important studies of neuroanatomy and comparative anatomy, as well as embryology, his name is rarely remembered by most medical historians. His name is linked to the nucleus he discovered: the Staderini nucleus or intercalated nucleus, a collection of nerve cells in the medulla oblongata located lateral to the hypoglossal nucleus. This article focuses on the biography of the neuroanatomist as well as the nucleus that carries his name and his other research, especially on comparative anatomy and embryology.

Neck muscle afferents influence oromotor and cardiorespiratory brainstem neural circuits

Sensory information arising from the upper neck is important in the reflex control of posture and eye position. It has also been linked to the autonomic control of the cardiovascular and respiratory systems. Whiplash associated disorders (WAD) and cervical dystonia, which involve disturbance to the neck region, can often present with abnormalities to the oromotor, respiratory and cardiovascular systems. We investigated the potential neural pathways underlying such symptoms. Simulating neck afferent activity by electrical stimulation of the second cervical nerve in a working heart brainstem preparation (WHBP) altered the pattern of central respiratory drive and increased perfusion pressure. Tracing central targets of these sensory afferents revealed projections to the intermedius nucleus of the medulla (InM). These anterogradely labelled afferents co-localised with parvalbumin and vesicular glutamate transporter 1 indicating that they are proprioceptive. Anterograde tracing from the InM identified projections to brain regions involved in respiratory, cardiovascular, postural and oro-facial behaviours—the neighbouring hypoglossal nucleus, facial and motor trigeminal nuclei, parabrachial nuclei, rostral and caudal ventrolateral medulla and nucleus ambiguus. In brain slices, electrical stimulation of afferent fibre tracts lateral to the cuneate nucleus monosynaptically excited InM neurones. Direct stimulation of the InM in the WHBP mimicked the response of second cervical nerve stimulation. These results provide evidence of pathways linking upper cervical sensory afferents with CNS areas involved in autonomic and oromotor control, via the InM. Disruption of these neuronal pathways could, therefore, explain the dysphagic and cardiorespiratory abnormalities which may accompany cervical dystonia and WAD.

The neurochemically diverse intermedius nucleus of the medulla as a source of excitatory and inhibitory synaptic input to the nucleus tractus solitarii

Sensory afferent signals from neck muscles have been postulated to influence central cardiorespiratory control as components of postural reflexes, but neuronal pathways for this action have not been identified. The intermedius nucleus of the medulla (InM) is a target of neck muscle spindle afferents and is ideally located to influence such reflexes but is poorly investigated. To aid identification of the nucleus, we initially produced three-dimensional reconstructions of the InM in both mouse and rat. Neurochemical analysis including transgenic reporter mice expressing green fluorescent protein in GABA-synthesizing neurons, immunohistochemistry, and in situ hybridization revealed that the InM is neurochemically diverse, containing GABAegric and glutamatergic neurons with some degree of colocalization with parvalbumin, neuronal nitric oxide synthase, and calretinin. Projections from the InM to the nucleus tractus solitarius (NTS) were studied electrophysiologically in rat brainstem slices. Electrical stimulation of the NTS resulted in antidromically activated action potentials within InM neurons. In addition, electrical stimulation of the InM resulted in EPSPs that were mediated by excitatory amino acids and IPSPs mediated solely by GABA(A) receptors or by GABA(A) and glycine receptors. Chemical stimulation of the InM resulted in (1) a depolarization of NTS neurons that were blocked by NBQX (2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonoamide) or kynurenic acid and (2) a hyperpolarization of NTS neurons that were blocked by bicuculline. Thus, the InM contains neurochemically diverse neurons and sends both excitatory and inhibitory projections to the NTS. These data provide a novel pathway that may underlie possible reflex changes in autonomic variables after neck muscle spindle afferent activation.

Nucleus prepositus

The cytoarchitecture and the histochemistry of nucleus prepositus hypoglossi and its afferent and efferent connections to oculomotor structures are described. The functional significance of the afferent connections of the nucleus is discussed in terms of current knowledge of the firing behavior of prepositus neurons in alert animals. The efferent connections of the nucleus and the results of lesion experiments suggest that it plays a role in a variety of functions related to the control of gaze.

Afferent pathways to the region of the vestibular nuclei that participates in cardiovascular and respiratory control

Prior experiments have shown that a region of the medial and inferior vestibular nuclei contributes to cardiovascular and respiratory regulation. In addition to labyrinthine inputs, the majority of neurons in this region of the vestibular nuclei receive signals from the skin, muscle, and viscera, although the pathways conveying these nonlabyrinthine inputs to the vestibular nucleus neurons are unknown. To gain further insight into the afferent pathways to this functionally distinct subdivision of the vestibular complex, we combined monosynaptic mapping with viral transneuronal tracing in the ferret. First order afferent projections were defined by retrograde transport of the beta-subunit of cholera toxin (CTbeta), and the extended polysynaptic circuitry was defined in the same animals by injection of a recombinant of pseudorabies virus Bartha (PRV) into the contralateral vestibular nuclei. Neurons containing CTbeta or infected by retrograde transneuronal transport and replication of PRV were distributed throughout the spinal cord, but were 10 times more prevalent in the cervical cord than the lumbar cord. The labeled spinal neurons were most commonly observed in Rexed's laminae IV-VI and the dorsal portions of laminae VII-VIII. Both the CTbeta and PRV injections also resulted in labeling of neurons in all four vestibular nuclei, the prepositus hypoglossi, the reticular formation, the inferior olivary nucleus, the medullary raphe nuclei, the spinal and principal trigeminal nuclei, the facial nucleus, and the lateral reticular nucleus. Following survival times >/=3 days, PRV-infected neurons were additionally present in nucleus solitarius and the gracile and cuneate nuclei. These data show that an anatomical substrate is present for somatosensory and visceral inputs to influence the activity of cells in the autonomic region of the vestibular nuclei and suggest that these signals are primarily transmitted through brainstem relay neurons.

Surgical treatment of greater occipital neuralgia: an appraisal of strategies

The surgical treatment of greater occipital neuralgia often involves diagnostic anesthetic blockade, followed by chemical or surgical ablation of the greater occipital nerve. The anatomy of this region was studied in microdissections of 2 cadaver specimens. The diagnosis and management of a series of 5 patients with greater occipital neuralgia is discussed. Two patients were treated with atlanto-epistrophic ligament decompression of the C2 dorsal root ganglion and nerve; four patients had C2 ganglionotomy performed. All patients in this series had immediate complete relief of pain following surgery. Patients were followed for a mean of 24 months (range 7-33 months). One patient had a recurrence of her original pain after 26 months following atlanto-epistrophic ligament decompression and required re-operation in the form of bilateral C2 ganglionotomy. All patients experienced transient nausea and dizziness in the several days following surgery. One patient had an incisional cerebrospinal fluid leak. Microsurgical C2 gangliotomy is advocated as the preferred surgical treatment of greater occipital neuralgia of idiopathic origin.

Characteristics of saccades induced by neck torsions: a re-examination in the normal guinea pig

Torsion of the neck relative to the fixed head results in several reflexes involving the eyes, the neck and the body. One of these reflexes, the cervico-ocular reflex, has been described as having a small gain in the normal animal. However, when the body of a guinea pig is moved relative to the fixed head with a ramp-like velocity profile, saccades are systematically elicited in the direction of body movement. We re-examined the characteristics of this reflex in the normal guinea pig and demonstrated that: (1) it occurs mainly in the range of high velocity body movements; (2) the latency of the saccades is shorter than previously suspected; (3) the saccades are triggered at specific positions relative to the starting and ending positions of rotation, revealing some degree of flexibility in the reflex. We hypothesize that these saccades of nuchal origin are under the control of the same neuronal circuit as visually triggered saccades and quick phases of vestibular nystagmus. Thus, this nuchal reflex may fundamentally subserve orienting behaviour in normal animal.

Autoradiographic localization of 5HT1 binding sites in autonomic areas of the rat dorsomedial medulla oblongata

Serotonin (5HT) binding sites in autonomic portions of the dorsomedial medulla oblongata of the rat were localized using autoradiographic techniques with radioactive ligands that express high affinity for the 5HT1 (3H-5HT), 5HT1A (3H-8OH-DPAT), or 5HT1B (125I-CYP with isoproterenol) receptor subtypes. 5HT1A sites were densely distributed in the nucleus tractus solitarius (NTS), with the highest densities localized to the interstitial subnucleus and the central subnucleus. 5HT1B sites were also found in the NTS, with the highest densities localized to the substantia gelatinosa subnucleus. The dorsal motor nucleus of the vagus nerve and nucleus ambiguus exhibited low densities of 5HT1B sites. However, the nucleus intercalatus, a cerebellar relay nucleus that also contains dendrites of vagal parasympathetic preganglionic neurons and receives autonomic forebrain afferent input, showed very dense 5HT1B sites. The promontorium, paratrigeminal islands, and the dorsomedial portion of the trigeminal nucleus (DM5), which are areas of viscerosomatic integration, exhibited high densities of both 5HT1A and 5HT1B sites. The area postrema contained low levels of both 5HT1A and 5HT1B sites. Visceral deafferentation via cervical vagotomy or nodose ganglionectomy caused a significant decrease in 5HT1A sites in the interstitial subnucleus of the NTS ipsilateral to the lesion. No changes were seen in 5HT1B sites. These studies suggest that 5HT1A and 5HT1B sites are involved in the processing of visceral sensory information in the NTS and associated areas. Based upon viscerotopic organization of the NTS, 5HT1A sites appear preferentially distributed in portions of the NTS that are associated with the coordination of swallowing, respiration, and cardiovascular function, while 5HT1B sites appear preferentially distributed in areas of the NTS associated with gastrointestinal, hepatic, pancreatic, and cardiovascular function. However, since these association were not absolute and there was a great deal of overlap between the two sites, speculation regarding their specific functions in autonomic control must await pharmacological examination.

Autoradiographic localization of 5HT1 binding sites in the medulla oblongata of the rat

Serotonin (5HT) binding sites in the medulla oblongata of the rat were localized using autoradiographic techniques with radioactive ligands that express high affinity for the 5HT1 (3H-5HT), 5HT1A (3H-80H-DPAT), or 5HT1B (125I-CYP with isoproterenol) receptor subtypes. 5HT1A sites were concentrated primarily in certain sensory regions of the medulla and in regions that contain serotonergic neurons. 5HT1B sites were diffusely distributed throughout the reticular formation and motor regions as well as being localized to certain sensory regions. A surprising finding was an association of 5HT1B binding sites with the corticospinal tract. 3H-5HT binding generally reflected the combined pattern of 5HT1A and 5HT1B sites but was also extremely dense in the choroid plexus, which exhibited virtually no 5HT1A or 5HT1B ligand binding. Presumably this binding, which was blocked by ketanserin, corresponds to 5HT1C sites. Administration of the serotonergic neurotoxin 5,7-dihydroxytryptamine reduced 5HT1A binding sites in regions of the medulla that contain serotonergic neuronal cell bodies. 5HT1B binding was not significantly altered in any area of the medulla. These studies indicate an important role for 5HT1A ligands in the processing of visceral and somatic sensory information, in regulation of certain cerebellar afferent projections, and in the regulation of serotonergic neuronal activity. 5HT1B ligands would be expected to regulate visceral and somatic efferent activity, as well as sensory information and reticular efferent activity, and might presynaptically regulate cortical inputs to the brain stem and spinal cord.

Central projections of cervical primary afferent fibers in the guinea pig: an HRP and WGA/HRP tracer study

The central course and the projections of the first and the second cervical dorsal root ganglia and of suboccipital muscle primary afferent fibers in the guinea pig were studied by means of anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA/HRP) or aqueous solution of horseradish peroxidase (HRP). Injections of WGA/HRP into the second cervical dorsal root ganglion produced labeling in the dorsal and ventral horns. Within the spinal cord, the largest amount of HRP reaction product was found within the lateral third of the substantia gelatinosa and within the central cervical nucleus. The main area of termination in the medulla was the external cuneate nucleus. However, HRP reaction product was also found within the medial and inferior vestibular nuclei, cell group x, the perihypoglossal nuclei, the nucleus of the solitary tract, and the nucleus of the spinal trigeminal tract. Descending fibers could be detected as caudal as spinal segment T5. Injections of WGA/HRP into the first cervical dorsal root ganglion produced heavy terminal label within the central cervical nucleus but not within the substantia gelatinosa. Again, the external cuneate nucleus was the main area of termination within the medulla. Label could not be observed within the vestibular nuclear complex or within the spinal trigeminal nucleus. Injections of aqueous HRP into the suboccipital muscles produced heavy transganglionic label within the central cervical nucleus, whereas the substantia gelatinosa totally lacked terminal label. Ascending proprioceptive fibers reached the external cuneate nucleus and group x. Scanty projections could be detected within the vestibular nuclei as well as within the perihypoglossal nuclei except for the nucleus prepositus hypoglossi. Label was absent in the spinal trigeminal nucleus.

A reinvestigation of the spinovestibular projection in the cat using axonal transport techniques

There are numerous discrepancies within the literature concerning the sources of spinovestibular fibers and their distribution in the vestibular complex. Sources of afferents from all spinal levels were sought using the retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase. Following injections of this tracer in all portions of the vestibular complex retrograde labelling was densest at upper cervical levels, especially within the contralateral central cervical nucleus. Labelling was also observed in laminae VI (ipsilaterally), IV, V, VII, and VIII (bilaterally). At progressively more caudal levels, numbers of labelled cells decreased but were similarly distributed in these laminae. The terminal distribution of spinal efferent fibers within the vestibular complex was revealed by injecting wheat germ agglutinin conjugated to horseradish peroxidase or tritiated amino acids into various levels of the spinal cord. These studies showed that all spinal levels project to the descending vestibular nucleus and group x. The f-tail of the descending vestibular complex receives projections from upper cervical and thoracic levels. Terminations within the medial vestibular nucleus arise from both upper cervical and lumbar levels. No conclusive evidence was found supporting the presence of substantial direct spinal projections to the lateral vestibular nucleus, superior vestibular nucleus, or group z. Possible functional roles for the spinovestibular projection in posture and gaze are discussed.

Central distribution of cervical primary afferents in the rat, with emphasis on proprioceptive projections to vestibular, perihypoglossal, and upper thoracic spinal nuclei

The projections of primary afferents from rostral cervical segments to the brainstem and the spinal cord of the rat were investigated by using anterograde and transganglionic transport techniques. Projections from whole spinal ganglia were compared with those from single nerves carrying only exteroceptive or proprioceptive fibers. Injections of horseradish peroxidase (HRP) or wheat germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) were performed into dorsal root ganglia C2, C3, and C4. Free HRP was applied to the cut dorsal rami C2 and C3, greater occipital nerve, sternomastoid nerve, and to the C1/2 anastomosis, which contains afferents from suboccipital muscles and the atlanto-occipital joint. WGA-HRP injections into ganglia C7 and L5 were performed for comparative purposes. Injections of WGA-HRP or free HRP into rostral cervical dorsal root ganglia and HRP application to C2 and C3 dorsal rami produced labeling in dorsal and ventral horns at the level of entrance, the central cervical nucleus, and in external and main cuneate nuclei. From axons ascending to pontine and descending to upper thoracic spinal levels, medial collaterals were distributed to medial and descending vestibular, perihypoglossal and solitary nuclei, and the intermediate zone and Clarke's nucleus dorsalis in the spinal cord. Lateral collaterals projected mainly to the trigeminal subnucleus interpolaris and to lateral spinal laminae IV and V. Results from HRP application to single peripheral nerves indicated that medial collaterals were almost exclusively proprioceptive, whereas lateral collaterals were largely exteroceptive with a contribution from suboccipital proprioceptive fibers. WGA-HRP injections into dorsal root ganglia C7 and L5 failed to produce significant labeling within vestibular and periphypoglossal nuclei, although they demonstrated classical projection sites within the brainstem and spinal cord. The consistent collateralisation pattern of rostral cervical afferents along their whole rostrocaudal course enables them to contact a variety of precerebellar, vestibulospinal, and preoculomotor neurons. These connections reflect the well-known significance of proprioceptive neck afferents for the control of posture, head position, and eye movements.

Distribution of external cuneate nucleus afferents to the cerebellum: I. Notes on the projections from the main cuneate and other adjacent nuclei. An experimental study with radioactive tracers in the cat

Transport of radioactive leucine was used to demonstrate cerebellar projections from the external cuneate nucleus (NCE) and from adjacent portions of the main cuneate nucleus (NC), of the spinal trigeminal nucleus (N.tr.sp.V) and of the vestibular nuclei. Projections from NCE and NC in part terminate over exclusive regions and in part overlap. After injections limited to NCE, labeling is found in all regions of the anterior lobe and lobule VI, in vermal lobules VII, VIII, and IX, and in medial regions of central folia of the paramedian lobule. Afferents from NC are observed in intermediate and lateral regions of lobules IV-VI, in lobules VIII and IX, in medial portions of crura I and II, and in lateral parts of central folia of the paramedian lobule as well as in its rostral folia. Afferents from N.tr.sp.V are distributed in lateral regions of lobules II-VI, in the rostral folium of lobule IX, in medial parts of crura I and II, and in rostral folia of the paramedian lobule. Afferents from the vestibular nuclei are present in vermal lobules VII, IX, and X and in the paramedian lobule. Projections from NCE are bilateral with ipsilateral predominance, whereas those from NC and N.tr.sp.V are ipsilateral. Projections from NCE are generally much denser than those from the other nuclei. Throughout the projection area, afferents from NCE are distributed in greater amounts in folia close to the medullary core and are much less dense near the surface. Afferents from the other nuclei do not show surface-to-depth density differences.